Optical pickup

Abstract

An optical pickup for irradiating a light beam onto an information recording medium and receiving a light reflected by the medium, includes a light source for emitting a light beam, and a liquid crystal panel for diffracting the light beam to produce a main beam and a plurality of sub-beams to be irradiated on the medium. The liquid crystal panel included a first area in which a first group of grating patterns with predetermined pitches is formed and a second area in which a second group of grating patterns having the predetermined pitches is formed, and the first group of grating patterns and the second group of grating patterns are arranged on a plane with a gap area formed between the first area and the second area so as to form an integrated grating pattern. The optical pickup further includes a control unit for applying a first voltage to the first area to control a refractive index of the first area and applying a second voltage to the second area to control a refractive index of the second area, thereby to control a diffraction characteristic of the integrated grating pattern.

What is claimed is:  
     
       1. An optical pickup for irradiating a light beam onto an information recording medium and receiving a light reflected by the medium, comprising: 
       a light source for emitting a light beam;  
       a liquid crystal panel for diffracting the light beam to produce a mean beam and a plurality of sub-beams to be irradiated on the medium, the liquid crystal panel comprising a first area in which a first group of grating patterns with first predetermined pitches is formed and a second area in which a second group of grating patterns having second predetermined pitches is formed, the first group of grating patterns and the second group of grating patterns being arranged on a plane with a gap area formed between the first area and the second area so as to form an integrated grating pattern, the first area comprising a first common area through which a voltage is supplied to all of the first group of grating patterns, the second area comprising a second common area through which a voltage is supplied to all of the second group of grating patterns; and  
       a control unit for applying a first voltage to the first common area to control a refractive index of the first area and applying a second voltage to the second common area to control a refractive index of the second area, thereby to control a diffraction characteristic of the integrated grating pattern.  
     
     
       2. The optical pickup according to claim  1 , wherein the control unit operates by selecting one of a first mode or applying both the first voltage and second voltage and second mode for applying either one of the first voltage and second voltage. 
     
     
       3. The optical pickup according to claim  1 , wherein said control unit operates by selecting one of a first mode for applying both the first voltage and second voltage, a second mode for applying either one of the first voltage and second voltage, and a third mode for applying neither the first voltage nor second voltage. 
     
     
       4. The optical pickup according claim  2 , wherein a direction and the pitch of the grating patterns are preset such that the main-beam is irradiated onto a recording track and the sub-beams are irradiated onto inter-tracks neighboring to the recording track on which the main-beam is irradiated in the second mode and the main-beam is irradiated onto a recording track and the sub-beams are irradiated onto the recording tracks neighboring to the recording track on which the main-beam is irradiated in the first mode. 
     
     
       5. The optical pickup according to claim  3 , further comprising a light receiving unit comprising first to fifth detectors arranged in a line, wherein the third detector receives the main-beam reflected by the recording track in the first to third modes, wherein the second and the fourth detectors neighboring the third detector receive the sub-beams reflected by the inter-tracks in the second mode, and wherein the first and the fifth detectors positioned outside of the second detector and the fourth detector, respectively, receive the sub-beams reflected by the neighboring tracks in the first mode. 
     
     
       6. The optical pickup according to claim  5 , wherein the first detector is a four-divided detector, and wherein the second detector and the fourth detector are two-divided detectors. 
     
     
       7. The optical pickup according to claim  1 , wherein the control unit comprises: 
       a liquid crystal driver for outputting the first voltage to the first area and outputting the second voltage to the second area; and  
       a controller for controlling the voltage outputted by the liquid crystal driver.  
     
     
       8. The optical pickup according to claim  7 , wherein the liquid crystal driver additionally outputs a reference voltage to the whole area of the liquid crystal panel including the first area, the second area and the gap area. 
     
     
       9. The optical pickup according to claim  1 , further comprising an objective lens for converging the main-beam and the sub-beams on the recording medium. 
     
     
       10. The optical pickup according to claim  1 , wherein the control unit operates by selecting one of a first mode for applying both the first voltage and second voltage thereby to form the integrated grating pattern of a first grating pitch, and a second mode for applying either one of the first voltage and the second voltage to form the integrated grating pattern of a second grating pitch, the second grating pitch being twice larger than the first grating pitch. 
     
     
       11. A method for irradiating a light beam onto an information recording medium and receiving light reflected by the medium, the method comprising: 
       transmitting a light beam into a liquid crystal panel having a first area of grating patterns with predetermined pitches of a first value and a second area of grating patterns with predetermined pitches of a second value, the first area and the second area being arranged on a plane with a gap area formed between the first area and the second area so as to form an integrated grating pattern;  
       controlling a first voltage applied to the first area so as to control a refractive index of the first area;  
       controlling a second voltage applied to the second area so as to control a refractive index of the second area;  
       directing light from the liquid crystal panel to the information recording medium; and  
       receiving light reflected from the medium.  
     
     
       12. The method according to claim  11 , wherein said step of transmitting a light beam into a liquid crystal panel produces a main beam and a plurality of sub-beams. 
     
     
       13. The method according to claim  12 , further comprising selecting a mode of operation, the mode of operation comprising: a first mode, wherein the step of controlling a first voltage applies a non-zero voltage to the first area and the step of controlling a second voltage applies a non-zero voltage to the second area; a second mode, wherein the step of controlling a first voltage applies a zero voltage to the first area and the step of controlling a second voltage applies a non-zero voltage to the second area or the step of controlling a first voltage applies a non-zero voltage to the first area and the step of controlling a second voltage applies a zero voltage to the second area; and a third mode, wherein the step of controlling a first voltage applies a zero voltage to the first area and the step of controlling a second voltage applies a zero voltage to the second area. 
     
     
       14. The method according to claim  13 , wherein the direction and pitches of the first area of grating patterns and second area of grating patterns are preset such selection of the second mode of operation provides that the main-beam is irradiated onto a recording track and the sub-beams are irradiated onto inter-tracks neighboring to the recording track and that selection of the first mode of operation provides that the main-beam is irradiated onto a recording track and the sub-beams are irradiated onto the recording tracks neighboring to the recording track on which the main-beam is irradiated. 
     
     
       15. The method according to claim  14 , wherein said step of receiving light reflected from the medium comprises receiving light with a light receiving unit including first to fifth detectors arranged in a line, wherein the third detector receives the main-beam reflected by the recording track when the first, second, or third mode is selected, wherein the second and the fourth detectors neighboring the third detector receive the sub-beams reflected by inter-tracks when the second mode is selected, and wherein the first and the fifth detectors positioned outside of the second detector and the fourth detector, respectively, receive the sub-beams reflected by the neighboring tracks when the first mode is selected. 
     
     
       16. The method according to claim  12  wherein the step of directing light from the liquid crystal panel comprises directing light into an objective lens for converging the main-beam and the sub-beams on the recording medium. 
     
     
       17. The method according to  13 , wherein the selection of a first mode of operation forms the integrated grating pattern with a first grating pitch and the selection of the second mode of operation forms the integrated grating pattern with a second grating pitch, the second grating pitch being twice larger than the first grating pitch.